Step 1: Make the Dough (Detrempe)
In a small bowl, dissolve the yeast in warm milk and let sit for 5–10 minutes until foamy.
In a large bowl or stand mixer, combine flour, sugar, and salt.
Add the softened butter and mix until crumbly.
Pour in the yeast-milk mixture and knead until a smooth dough forms, about 5–6 minutes.
Shape into a rectangle, wrap in plastic, and refrigerate for at least 1 hour.

Step 2: Prepare the Butter Block (Beurrage)
Place cold butter between two sheets of parchment paper.
Use a rolling pin to pound and shape the butter into an even 6×6-inch square.
Lightly dust with flour to prevent sticking.
Chill the butter in the fridge until firm but pliable (not rock hard).

Step 3: Enclose the Butter
On a lightly floured surface, roll out the chilled dough into a 10×10-inch square.
Place the butter block in the center on a diagonal so it looks like a diamond.
Fold the corners of the dough over the butter, meeting in the center like an envelope.
Pinch the edges to seal the butter inside completely.

Step 4: First Fold (Single Turn)
Roll the dough into a long rectangle, about 8×24 inches.
Fold the top third down, then the bottom third up over it (like a letter).
Rotate the dough 90 degrees, wrap in plastic, and refrigerate for 30–45 minutes.

Step 5: Second & Third Folds
Repeat the rolling and folding process two more times.
Be gentle to avoid breaking the dough and exposing the butter.
Always chill for 30–45 minutes between folds to maintain distinct layers.

Step 6: Final Roll & Shape
After the last fold and rest, roll the dough into a large rectangle, about 10×20 inches and ¼-inch thick.
Use a knife or pizza cutter to trim the edges for clean lines.
Cut into long triangles (about 5 inches wide at the base, 8 inches tall).
Make a small slit at the base of each triangle and roll tightly toward the tip to form a crescent shape.
Place on a parchment-lined baking sheet, tip side down.

Step 7: Proof the Croissants
Cover loosely with plastic wrap or a clean towel.
Let rise at room temperature for 1.5 to 2 hours, or until noticeably puffy and jiggly (not doubled in size).
If your kitchen is cool, place them in a turned-off oven with a bowl of warm water to create a warm proofing environment.

Step 8: Apply Egg Wash
Preheat your oven to 400°F (200°C).
Beat the egg with 1 tbsp of milk or water.
Brush each croissant gently with egg wash, making sure not to deflate them.

Step 9: Bake
Bake for 18–22 minutes until golden brown, crisp, and flaky.
Rotate the tray halfway through baking for even browning.
Let cool slightly before serving.